diff --git a/README.md b/README.md
index 57e8275..5027cda 100644
--- a/README.md
+++ b/README.md
@@ -68,8 +68,7 @@ yaml_export = tool_object.export_string()
 tool_object.export()
 
 # print to file
-with open("echotool.cwl", "w") as f:
-    tool_object.export(f)
+tool_object.export("echotool.cwl")
 ```
 
 ## References
diff --git a/cwlgen/requirements.py b/cwlgen/requirements.py
index 97ac701..6f5408a 100644
--- a/cwlgen/requirements.py
+++ b/cwlgen/requirements.py
@@ -23,6 +23,9 @@ def __init__(self, req_class):
     def get_class(self):
         return self._req_class
 
+    def __hash__(self):
+        return hash(self.get_class())
+
     @classmethod
     def parse_dict(cls, d):
 
diff --git a/examples/readme_example.py b/examples/readme_example.py
index ce50a85..e41f38c 100644
--- a/examples/readme_example.py
+++ b/examples/readme_example.py
@@ -15,3 +15,5 @@
 
 # print to console
 tool_object.export()
+
+tool_object.export("echotool.cwl")